Improve usage of window rectangles

src/gpu/GrScissorState.h

Index: src/gpu/GrScissorState.h
diff --git a/src/gpu/GrScissorState.h b/src/gpu/GrScissorState.h
new file mode 100644
index 0000000000000000000000000000000000000000..59ea088078ca9e0038cb7648687b6b9a2d620636
--- /dev/null
+++ b/src/gpu/GrScissorState.h
@@ -0,0 +1,40 @@
+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef GrScissorState_DEFINED
+#define GrScissorState_DEFINED
+
+#include "SkRect.h"
+
+class GrScissorState {
+public:
+    GrScissorState() : fEnabled(false) {}
+    GrScissorState(const SkIRect& rect) : fEnabled(true), fRect(rect) {}
+    void setDisabled() { fEnabled = false; }
+    void set(const SkIRect& rect) { fRect = rect; fEnabled = true; }
+    bool SK_WARN_UNUSED_RESULT intersect(const SkIRect& rect) {
+        if (!fEnabled) {
+            this->set(rect);
+            return true;
+        }
+        return fRect.intersect(rect);
+    }
+    bool operator==(const GrScissorState& other) const {
+        return fEnabled == other.fEnabled &&
+                (false == fEnabled || fRect == other.fRect);
+    }
+    bool operator!=(const GrScissorState& other) const { return !(*this == other); }
+
+    bool enabled() const { return fEnabled; }
+    const SkIRect& rect() const { return fRect; }
+
+private:
+    bool    fEnabled;
+    SkIRect fRect;
+};
+
+#endif